The scarifying of the inside of in situ pipes requires the movement of a hydrodemolition apparatus (hereafter called a “rig”), comprising a high pressure nozzle assembly, along the length of the pipe.
According to a typical prior art approach illustrated in FIG. 1, the rig 10 is attached to a hose 12 supplying high pressure fluid to the rig from the downstream end 14 of the pipe to be treated. The rig is attached to a winch cable 16 that extends from the rig to the upstream end 18 of the pipe, where the winch 20 is located. The winch gradually draws the rig from the downstream end to the upstream end of the pipe in a scarifying pass through the pipe to remove a layer 22, while the rig nozzles 24 are operated to scarify the inside of the pipe. The fluid supply hose 12 is fed from the opposed pump 26 side of the pipe, into the pipe and to the rig from the downstream end of the pipe. As the rig is drawn by the winch, the rig in turn draws the hose into the downstream end of the pipe.
Once the length of hose available on the pump side is exhausted, the hose will resist the forward movement of the rig in the pipe, causing it to stall in one spot while the nozzles are still operating. Once that is detected, the rig is stopped and an additional length of hose is attached to the end of the first length of hose. Movement of the rig can then be restarted to continue treatment of the inside of the pipe. Such stalling of the rig results in a phenomenon sometimes referred to as barbershop striping along the inside of the pipe. Personnel are often positioned inside the pipe to try to manage the hose feed to the rig and to avoid barbershop striping.
It is also known to follow the scarifying pass with a cleaning pass through the pipe using lower pressure fluid and consequently a different nozzle assembly that is swapped out of the rig, or by using a different rig entirely. The cleaning pass is typically accomplished using essentially the same method as for the scarifying pass and prepares the inside of the pipe for further operations such as painting or coating.
Once the pipe has been completely treated, the other operations such as painting or recoating the interior of the pipe can be completed, sometimes by a different crew or a different contractor.
The scarifying pass is performed in some cases by what is known as an ultra-high pressure nozzle assembly, using pressure is in the range of 40,000 psi. The cleaning pass is often performed using lower pressures in the range of 10,000 to 20,000 psi.
The prior art suffers from certain deficiencies. The barbershop striping produces an inconsistent treatment of the inside of the pipe. Personnel are required to assist and monitor the hose attachment to the rig. In addition, the treatment process, including two passes through the pipe, is time consuming. When other contractors await access to the pipe on a usually tight timeline, processing time must be minimized. This becomes inconvenient when dealing with particularly long sections of pipe that may take many days or weeks to complete, if they may be accomplished at all using the prior art approaches. Where a long length of pipe is involved, the drawing of the hose into the pipe by drawing the rig attached to the hose can become particularly challenging, requiring very powerful winches.
In an alternative prior art approach, the rig may be installed at one end of the pipe and may be towed by the hose itself which is drawn to a hose reel by a winch. However, this method of towing the rig tends to cause the rig to jerk inconsistently.
Another known approach is to have a tractor-driven rig inside the pipe. The rig progresses down the pipe while scarifying it, with the hose trailing the rig. Typically personnel are present in the pipe to periodically pull the hose in behind the rig. Alternatively the rig may be equipped with a winch to draw the hose behind it. In such case, personnel is still required in the pipe to ensure that the connection of the hose to the rig is not compromised by the tension on the hose, and to avoid the hose causing the rig to stall.
The invention provides an apparatus and the method that represent an improvement over the prior art. The scarifying of the inside of the pipe is accomplished more efficiently and more quickly to free up access to the treated section of pipe and the need for in-pipe personnel to deal with the hose is avoided.